Various methods are known in the art for optical 3D mapping, i.e., generating a 3D profile of the surface of an object by processing an optical image of the object. This sort of 3D profile is also referred to as a 3D map, depth map or depth image, and 3D mapping is also referred to as depth mapping.
Some methods of 3D mapping use time-of-flight sensing. For example, U.S. Patent Application Publication 2013/0207970, whose disclosure is incorporated herein by reference, describes a scanning depth engine, which includes a transmitter, which emits a beam comprising pulses of light, and a scanner, which is configured to scan the beam, within a predefined scan range, over a scene. The scanner may comprise a micromirror produced using microelectromechanical system (MEMS) technology. A receiver receives the light reflected from the scene and generates an output indicative of the time of flight of the pulses to and from points in the scene. A processor is coupled to control the scanner and to process the output of the receiver so as to generate a 3D map of the scene.
Another example of a time-of-flight scanner using MEMS technology is the Lamda scanner module produced by the Fraunhofer Institute for Photonic Microsystems IPMS (Dresden, Germany). The Lamda module is constructed based on a segmented MEMS scanner device consisting of identical scanning mirror elements. A single scanning mirror of the collimated transmit beam oscillates parallel to a segmented scanning mirror device of the receiver optics.
PCT International Publication WO 2014/016794, whose disclosure is incorporated herein by reference, describes optical scanners with enhanced performance and capabilities. In a disclosed embodiment, optical apparatus includes a stator assembly, which includes a core containing an air gap and one or more coils including conductive wire wound on the core so as to cause the core to form a magnetic circuit through the air gap in response to an electrical current flowing in the conductive wire. A scanning mirror assembly includes a support structure, a base, which is mounted to rotate about a first axis relative to the support structure, and a mirror, which is mounted to rotate about a second axis relative to the base. At least one rotor includes one or more permanent magnets, which are fixed to the scanning mirror assembly and which are positioned in the air gap so as to move in response to the magnetic circuit. A driver is coupled to generate the electrical current in the one or more coils at one or more frequencies selected so that motion of the at least one rotor, in response to the magnetic circuit, causes the base to rotate about the first axis at a first frequency while causing the mirror to rotate about the second axis at a second frequency.
U.S. Patent Application Publication 2014/0153001, whose disclosure is incorporated herein by reference, describes an optical scanning device that includes a substrate, which is etched to define an array of two or more parallel micromirrors and a support surrounding the micromirrors. Respective spindles connect the micromirrors to the support, thereby defining respective parallel axes of rotation of the micromirrors relative to the support. One or more flexible coupling members are connected to the micromirrors so as to synchronize an oscillation of the micromirrors about the respective axes.
U.S. Pat. No. 7,952,781, whose disclosure is incorporated herein by reference, describes a method of scanning a light beam and a method of manufacturing a microelectromechanical system (MEMS), which can be incorporated in a scanning device. In a disclosed embodiment, a rotor assembly having at least one micromirror is formed with a permanent magnetic material mounted thereon, and a stator assembly has an arrangement of coils for applying a predetermined moment on the at least one micromirror.